1. Field of the Invention
This invention relates to a device for repelling birds and more particularly to such a device which employs a rod having a permanent magnet assembly mounted thereon which is mounted for freedom of sideways motion universally in any direction in response to the wind thereby generating a varying magnetic field.
2. Description of the Related Art
Birds such as crows, sparrows, pigeons, thrushes and the like can be troublesome in scavenging rubbish, pecking at crops on farms and dropping feces. Conventional techniques for repelling birds include the generation of loud sounds, the use of signs with large eyes,etc. It has been found that birds sense terrestrial magnetic fields and use such fields in locating their position. This is described, for example on pages 130-134 of Bird Migration by Chris Mead published by Facts on File, Inc. in 1983. When they detect magnetic fields different from and stronger than terrestrial fields, they tend to become fearful and disoriented and take aversive action. Thus, birds tend not to approach any area where there is a magnetic field stronger than the terrestrial magnetic field.
Taking advantage of the above factors, various devices have been developed in the prior art which generate magnetic fields to repel birds. Such devices are described in Japanese Official Gazette, laid open patent no. Heisei-8-986612 and laid open patent no. 8-38022 and U.S. Pat. No. 5,353,543 issued Oct. 11, 1994 to K. Teraoka.
In these disclosures, devices are described which utilize miniature windmills which have magnets mounted on their rotatable vanes. Thus, variable magnetic fields are generated with the rotation of the windmill vanes to produce the desired end effect. Also described in one of these disclosures is a device employing a plurality of spherical magnets which are hung along a line across the entrance of a space to be protected. Such prior art devices have the disadvantage of occupying more space than to be desired. Further the construction, particularly of the windmill devices tends to be rather expensive. It is also to be noted that birds often fly into and nest within the structural beams of an iron tower which supports power lines where the power lines and the structure of the tower make it difficult to mount the types of devices of the prior art. If the magnetic repelling device is mounted outside of the tower structure and interlacing wires, the magnetic field generated thereby may not reach within the structure. Further, the steel structure of the towers tends to absorb the magnetic energy such that the effective range of the magnetic repelling device is limited.
Thus, with devices of the prior art, it is difficult to prevent birds from flying into and nesting in spaces confined between the structure of towers and the like. It is further to be noted that most such prior art devices have a fixed structure which cannot readily be adapted in size and shape for mounting in various different locations.